It ends up that I have overreacted at the first moment, my apologize to the API team. Experience which I described above is happening if I use "ads block" option, or if I use Brave browser with ads blocker. If I try with regular Chrome or FF, everything is ok.
I found the culprit for this: it ends up that I have used old key and base URL (before integration with windy.com). It worked fine few months but not any more. With new key and new base URL: https://api.windy.com/api/webcams/v2/, everything works fine.
Okay, I think I misunderstood the the response data. I'm guessing total refers to the total number of webcams, and the regions field lists all of the available regions. In which case, this is definitely enough.
I stand corrected.. the foto-webcam.eu cameras already ARE in windy
they were announced through webcam.travel and hence got onto windy